supra top speed

My car (92 7mgte was auto, now converted to 5 speed) Tops out 5 gear at 6k rpm at around 145-150 ish.. I thought for the longest time that i had a 4:11 Gear Ratio. I Through my info into the vin lookup at work and it says i have a 3:73. How is it possible that im topping out that low on such a...